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Paul Scherrer Institut Home News Experience OPTIS Technique R&D PROSCAN Q&A Tour

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Research and development

There is room for improvement in the functionality of the spot-scanning technique developed at PSI. Therefore, in tandem with the increase in medical uses for proton therapy, the gantry and its beam guiding and application techniques are being optimized. In particular the scanning speed and the sensitivity of the dynamic beam to organ motion (for example from breathing) during the treatment are being optimized.
With the current system the target volume (tumor plus safety margins) is only checked once during each radiation fraction. Due to this technical limitation only tumors which don’t move, such as those in the head and neck, spine and pelvis can be treated with optimal precision. For an expansion of the medical indications to lung and mammary carcinomas the entire target volume must be scanned 10-20 times faster. This should be repeatable within the same radiation period.


The new Gantry 2 features ultrafast scanning with a second magnetic axis which is vertical and located in the gap before the 90° magnet. Further efficiencies are achieved by guiding the intensity of the beam directly with the ion source from the dedicated COMET accelerator by means of a vertical deflector-plate. In the new PROSCAN facility it is possible to apply the dose with more precision as the energy of the beam can be dynamically varied with laminated magnets. Tests have shown that it will be possible to scan a half liter tumor mass in about 7 to 10 seconds.

To fulfil clinical requests, the design of the new gantry makes it possible to radiate tumors from nearly all sides. Incorporated in the new design is a floor around the patient table ensuring that during the treatment, the patient is always accessible to medical staff.

The goal of all these developments is to increase radiation precision of even moving tumors so that the PSI spot-scanning method becomes a viable alternative to the passive scattering-foil technique also for moving tumors. The compact gantry design could then replace the giant 10-12 m diameter gantries currently in construction and operation.